September 19, 2013

African Dust Clouds Could Be Affecting International Air Quality, Hurricanes

Dust clouds originating in Africa’s Sahara Desert can travel thousands of miles, impacting in the air quality in Texas and other regions of the world, according to research appearing in a recent edition of the journal Environmental Science and Technology.

In fact, not only can this phenomenon occur, but it does so every year – and the dust often reaches the US in large quantities, according to Joseph Prospero, professor emeritus at the University of Miami Rosenstiel School of Marine and Atmospheric Science and colleagues from the University of Houston and Arizona State University.

Prospero’s team found that average air concentration of inhalable particles more than doubled during a major Saharan dust intrusion in the city of Houston. They were able to distinguish between native dust particles and those transported across the Atlantic Ocean, essentially establishing a “fingerprint” for the African dust.

“To their knowledge, this is the first study that isolates, differentiates, and quantifies the air contaminants in the US during the incursion of African dust,” the Florida-based university said in a statement. “There is a concern that the fine airborne dust particles could be a health problem for asthmatics and people with respiratory problems.”

“Current EPA air quality standards are based on the total amount of particles that are in the air,” Prospero explained. “Our study will contribute to our ability to discriminate and identify the dominant components in the air during long-range transport events. Our hope is that our work is instrumental in assisting regulatory agencies respond to health and environmental issues linked to African dust.”

The Prospero team’s findings also look to address similar African dust intrusions impacting other parts of the world. For example, the authors report that enormous amounts of the African dust reaches the Caribbean Basin each year. In addition to harming the region’s air quality, the Saharan air could also have an effect on hurricane activity in the island region located southeast of North America, they caution.

“African dust storms are associated with hurricane season because the meteorological situations that are involved with generating tropical cyclones are also associated with the generation and transport of dust,” said Prospero. “The dust emerges from the coast of Africa in a hot, dry, elevated layer – the Saharan Air Layer (SAL) following behind Easterly Waves from which tropical cyclones sometimes develop. The SAL interacts with the waves in complex way, so that the relationship is not entirely clear. It is the subject of much ongoing research.”

Furthermore, dust that is suspended in the wind can absorb and scatter solar radiation, causing less sunlight to reach the ocean surface and causing cooler temperatures in the tropical Atlantic Ocean. This is the primary region where hurricanes develop, and cooler waters means there is less energy for hurricanes to form and strengthen. Prospero said that this phenomenon could contribute to 2013’s “unusually weak” hurricane season.

“The question is what happens with climate change. Although much of North Africa is expected to get drier, which would mean more dust, models can't agree on whether the climate in the current major dust sources will get drier or wetter in the future,” he added. “We are still trying to understand what drives these differences and the possible impacts.”